The present invention relates to a novel process for preparing hydrazodicarbonamide (xe2x80x9cHDCxe2x80x9d) which is, after oxidation to azodicarbonamide (xe2x80x9cADCxe2x80x9d), used as a polymerization auxiliary (Ullmann""s Encyclopaedia of Industrial Chemistry, Vol. A13, 185).
It is generally known that HDC is obtained from the reaction of hydrazine with urea (Ullmann""s Encyclopaedia of Industrial Chemistry, Vol. A13, 185). The yields in this process are good. However, hydrazine is relatively expensive since it is prepared by chlorination of ammonia and is also classified as a hazardous substance.
It is also known that hydrazine can be obtained from the reaction of ammonia and hydrogen peroxide in the presence of ketones and catalysts. However, the yields leave something to be desired. (Ullmann""s Encyclopaedia of Industrial Chemistry, Vol. A13, 182).
Furthermore, it is known that benzophenonimine can be oxidized using oxygen in the presence of catalysts to give benzophenonazine, however, which can be cleaved only with strong acids such as sulfuric acid to form hydrazinium sulfate (Catal. Rev. CR Sci. Eng., 1990, 32, 229-277). The direct reaction of this benzophenonazine with urea to form HDC is, however, not successful.
It has now been found that hydrazodicarbonamide (xe2x80x9cHDCxe2x80x9d) of formula (I) 
can be prepared by a process comprising
(a) reacting aliphatic ketones of formula (II) 
xe2x80x83wherein
R1, R2, and R3 are identical or different and are each substituted or unsubstituted alkyl, and
R4 is hydrogen, substituted or unsubstituted alkyl, or substituted or unsubstituted cycloalkyl, or
R1 together with R2 or R4 form an alkylene chain,
xe2x80x83with ammonia under pressure to form ketimines of formula (III) 
xe2x80x83wherein
R1, R2, R3 and R4 are as defined above,
(b) oxidizing the ketimines of formula (III) with oxygen in the presence of catalysts to form ketazines of formula (IV) 
xe2x80x83wherein
R1, R2, R3 and R4 are as defined above, and
(c) reacting the ketazines of formula (IV) with urea and water in the presence of catalysts.